What is Switch-mode Power Supplies (SMPS)

Switch-mode Power Supplies, are electronic power equipment, which include switching controller, for converting electric power to another voltage level. Switch-mode Power Supplies (SMPS) like other power supplies can be connected to one bigger source and transform energy to loads by different currents and voltages. Unlike linear power supplies, power transistors of switch-mode Power Supplies turn on and off, constantly, and as a result, these equipment have minimum loss power. According to duty cycle, Output voltage of switch mode power supplies is performed. High efficiency and minimum loss power are the main advantages of SMPS

History of switch mode power supply (SMPS)

Electrical engineers had presented the idea of switch mode power supplies (SMPS) in 1970. The efficiency of switch mode power supplies was low in last decades. Output powers of SMPS are more than batteries and analog power supplies, while their weight and volume are lower.These days, Switch mode power supplies are produced in different types. In next figure, one type of SMPS which includs cooling liquid system is shown.

different types of SMPS

Different types of Switch mode power supplies :
- Forward SMPS-Fly back SMPS
Although Their similarities are a lot, but they have some special differences.
The placement of magnet element determine the type of power supply.
Main elements of power supplies are:
- Source for making PWM wave
- Inductor (for advanced sources transformer would be used instead of inductor)
- Power Transistors
- Capacitance for energy storage in output
- feedback and sensing network

forward switching power supply

The circuit of forward switching power supply is shown in next figure. When the switch is open, through diode the current flows. In next cycle, by closing the switch, energy achieved to inductor.

Flyback switching power supply

The circuit of flyback power supply is shown in next figure. By closing the switch, the current flows to inductor. By opening the switch, the capacitor would be charged and the load is supplied.

DC converters

For converting voltage level to another voltage level, when the output power is low, analog circuits for increasing or decreasing the voltage level are applied. But for higher output powers, the switch mode power supplies should be used.Some switch mode power supplies have capability to supply from both ac and dc voltages and convert it to the required dc voltage. SMPS can be produced based on input type (single phase, two phase, three phase) for different voltage and current ranges. J.Schneider and Ziegler are the big producers of SMPS products. some SMPSof these Produces are shown in below figure.

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